A radio communication system has been evolved to provide various high-speed large-capacity services to Mobile Stations (MSs), and a typical example of the radio communication system may include a Long-Term Evolution (LTE) mobile communication system, a Long-Term Evolution Advanced (LTE-A) mobile communication system, an Evolved Packet System (EPS), and an Institute of Electrical and Electronics Engineers (IEEE) 802.16m communication system.
As the radio communication system has been evolved, MSs have been also evolved to enable receiving various high-speed large-capacity services, and specially to be a smart phone. As a smart phone market has been grown, a demand for a voice service through a WLAN module equipped in a smart phone has been greatly increased.
In an enterprise WLAN environment, the number of MSs which access a particular Access Point (AP) has been increased as a demand for a voice service through a Fixed Mobile Convergence (FEM) service has been increased. So, there is a need for one AP to simultaneously provide a plurality of MSs with a voice service.
A WLAN system uses a Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) protocol for a medium access, and an Enhanced Distributed Channel Access (EDCA) scheme for guaranteeing Quality of Service (QoS).
The EDCA scheme uses a distributed access scheme for an access to radio resources, so an overhead for avoiding a collision and acquiring synchronization are relatively large. The overhead includes back-off delay necessary per each data packet transmission, a physical (PHY) preamble transmission, a PHY header transmission, an acknowledgement (ACK) frame transmission, etc. In a packet network system such as a WLAN system, efficiency of the EDCA scheme becomes worst for a voice service such as a Voice over Internet Protocol (VoIP) service on which traffic with a relatively small size occurs every period. A VoIP service capacity per AP becomes limited due to a sharp decline for efficiency of the EDCA scheme, so a packet network performance becomes decreased.